1. Field of the Invention
This invention relates to optical fiber connectors, and, in addition, to optical fiber connector bodies, optical fiber holders, and combinations thereof. Accordingly, it is a general object of this invention to provide new and improved devices of such character.
2. Description of the Prior Art
With some exceptions, including those listed below, previous fiber optic connectors essentially have been devices for physically bringing the ends of two fibers together so closely and accurately as to minimize the disturbance of the optical waveguide geometry of the fibers as light passes from one to the other.
Known exceptions use lenses of various types to project an image of each fiber end onto the end of the other:
a. discrete conventional lenses with the fiber positioned at the focal point of the lens, and air between the fiber and the lens, as suggested by M. A. Bedgood, J. Leach, and M. Matthews, "Demountable Connectors for Optical Fiber Systems", Electr. Commun. (U.K.), Vol. 51, pp. 85-90, 1976, PA1 b. glass sphere with high index of refraction (n=2), with the fiber butted against the sphere, on axis with the center of the sphere, as suggested by N. Nicia, "Practical Low-Loss Lens Connector for Optical Fibers", Electronics Lett., Vol. 14, pp. 511-512, August 1978, and PA1 c. a quarter-pitch gradient-index rod lens, with the fiber butted against the rod, and its axis aligned with the axis of the rod, as suggested by recent published articles by Nippon Telephone & Telegraph of Japan on applications of such graded-index lenses. A specific reference to their use in connectors was not found in such articles. PA1 a. a discrete lens must be carefully aligned in a connector housing, with its optical axis oriented with the axis of the connector, and then a fiber must be manipulated to be on the same axis, with its end at the focal point: also, the fiber and lens have three glass-to-air interfaces which must be anti-reflection coated to achieve minimum losses, PA1 b. the sphere technique requires an optical lens-quality complete sphere (not to be confused with conventional "spherical lenses", whose surfaces are small segments of a sphere), with an index of refraction of exactly 2.00, in order for the focal point to be on the surface of the sphere. Furthermore, butting a fiber to the surface of such a sphere automatically determines the focal point only after first aligning the fiber laterally and angularly along the axis of the sphere and the connector body, and PA1 c. a gradient-index rod lens has the same alignment problems as above, and in addition is difficult and expensive to manufacture with an appropriate index profile for adequate imaging. PA1 a. can be manufactured entirely of a few inexpensive molded parts, PA1 b. provides connections of extremely low insertion loss, even with small-diameter glass communications-grade fibers, PA1 c. is largely insensitive to minor scratches and dirt on ends, PA1 d. is tolerant to lateral displacement alignment errors, (many fiber diameters offset), PA1 e. is insensitive to axial separation of connector halves (up to several centimeters), PA1 f. can optimally interconnect fibers with different diameters and/or numerical apertures, and PA1 g. can be quickly and easily field-installed with only a fiber cleaver and epoxy (no microscopes, jigs, adjustments, etc.).
In each of the foregoing, light diverges from a relatively point-like fiber end and is collimated by a lens. Conversely, the collimated light beam is refocused by a lens onto an end of a second fiber.
Disadvantageously, many prior art optical fiber connectors involve physically bringing two fiber ends together. Except for those situations involving very large diameter fibers, extreme mechanical tolerances have been required. The competing requirements of close tolerances on one hand, and permitting a large number of connect-disconnect cycles with little degradation on the other hand, are exceptionally difficult to achieve in the same device. In particular, connectors intended for small core communications-grade fibers with less than 1 dB loss are believed to have been possible only by using very expensive individually machined and aligned parts. They usually cannot be reliably installed in the field. In addition, the small fiber ends must be kept clean and free from scratches, or the optical throughput efficiency decreases rapidly.
Also, disadvantageously, high-quality field installation of the fiber to the connector body is not achievable for the three imaging-type connectors discussed above. In addition, other intrinsic disadvantages are present:
The published prior art includes various U.S. patents which may be of interest.
U.S. Pat. No. 4,056,305 to McCartney et al describes a connector having a deformable elastomeric alignment element having a bore therethrough. Two sets of three equal diameter cylindrical rods are mounted in opposite ends of the bore so as to define a space therebetween for receiving an optical fiber. The rods have an interference fit in the central portion of the bore so that compression of the rods results in laterally aligning the fibers.
U.S. Pat. No. 3,948,582 to Martin discloses an optical fiber connector with separately formed bodies of substantially elongated form. Each body has an axial bore in which the optical fibers can be fitted. The end of one body defines a socket adapted to mate with a plug-shaped end of the second body.
U.S. Pat. No. 3,734,594 to Trambarulo describes an optical fiber splicer having a deformable angular core disposed between a pair of metallic pressure plates. The fibers to be spliced are inserted into opposite ends of the core and a longitudinal force applied to the plates causes the core to deform radially, thereby securing the fibers.